They're quite common. In other words, no extra value. I started error hunting recently and have found that very thing in every denomination of coin, including the presidential dollars. It "might" be worth a little something more if the effect is on both sides, but not on one - unless part of the printing/image is off the coin.
Have found lots of interesting finds from my first box of cents. Don't yet know if any are worth anything, but they ARE interesting.